1. Field of the Invention
The present invention relates to vehicle ride struts and more particularly to ride struts for load carrying vehicles operable over rough terrain.
2. The Prior Art
Vehicle ride struts are generally positioned between the vehicle frame and an axle housing, or equivalent structure, to act as a suspension spring enabling relative motion between the frame and vehicle wheels when rough terrain is encountered.
The ride struts have frequently been formed by telescoping tubular housings having a compression spring confined between them. The closed ends of the housings are connected to the respective frame and axle housing so that as the axle tends to move toward the frame the spring is further compressed. The compression springs are initially compressed by the sprung vehicle weight and payload.
One problem in some prior art ride struts resulted from a vehicle wheel encountering a depression, chuck hole or the like of sufficient depth that the ride strut was fully extended with the wheel and axle suspended from the frame principally by the ride strut. The ride strut housings tended to be hyperextended and damaged in such circumstances because of the abruptly applied load of the wheel and axle and the application of ride strut spring forces to the strut housing members.
In order to reduce the possibility of strut damage, ride strut constructions were proposed in which a portion of the ride strut spring was resiliently compressed when the ride strut was extended more than a predetermined amount. The spring compression, in effect, provided for resilient hyperextensions of the struts and tended to ameliorate shock loadings applied to the strut housing members. The prior art proposals employed snubbers formed by spring compressing piston-like members disposed in the ride struts and supported by associated rods extending at least part way through the strut. An example of one such ride strut construction is disclosed by U.S. Pat. No. 3,713,666 issued to Cheers et al.
The Cheers et al. patent discloses a ride strut spring constructed from a stack of stiffly resilient "doughnuts." Each "doughnut" is a spring unit formed by a rubber-like material bonded to an annular supporting plate. Springs constructed in this manner have proved relatively successful because they can provide tolerable spring characteristics under extreme load conditions without necessitating unduly large ride struts.
In ride struts constructed with snubbers the internal rod and associated piston enabled compression of all the spring units under normal vehicle loads and compression of a portion of the spring units when the strut was extended. These types of struts dealt with the hyperextension problems but had some constructional drawbacks. In the first place the use of an internal rod necessitated the use of open centered spring units which, because of their open centers, did not have the spring capacity of an otherwise identical spring unit having spring material along its centerline. The struts therefore tended to be of greater size than they might otherwise have been. Secondly the annular shaped spring units tended to become skewed in the ride struts which resulted in damage to the rod, the ride strut housing members and to the spring units. The rods were carefully constructed to guide the relatively moving spring units but even so, scoring, abrasion, etc., of the ride strut components was not always avoidable. In some proposals additional spring units were employed to avoid metal to metal contact between ride strut components when the ride strut rebounded from a hyperextended position to a normally compressed position. Additionally the construction of these units required a significant number of machined component parts, or parts which were otherwise not easily fabricated, resulting in the ride struts being complicated to manufacture and expensive.